"Virtual reality" and "telepresence" have become extremely popular for use in research, industrial and entertainment applications. In "virtual reality", or VR, a user is permitted to view a computer-generated graphical representation of a selected environment. Depending on the sophistication of the hardware and software used to generate the virtual reality environment, the user may be treated to a three dimensional view of the simulated environment. In "telepresence," a user is permitted to view a real-world, live or recorded environment from a three dimensional perspective.
In addition, in some higher end systems the user is permitted to see different portions of the VR and telepresence environments simply by moving or orienting his head in one or more degrees of freedom. This permits the user to obtain the sensation that he is immersed in the computer-generated/real-world environment. High end devices detect pan, roll and tilt motions by the user and cause the environment to change accordingly. The pan.backslash.tilt.backslash.roll motions may be inputted by many types of input devices, such as joysticks, buttons or head orientation sensors (which may be connected to head mounted displays).
In VR applications, a continuing problem is how to render a three dimensional environment of the quality and speed users want while offering the product at a price they can afford. To make a realistic environment, such as in a three dimensional video game, many three dimensional polygons need to be rendered. This rendering requires prohibitively expensive hardware which greatly restricts the commercial value of such a system.
In relation to telepresence applications, a continuing problem with the prior art is how to encode sufficient data that a viewer may arbitrarily move his viewing perspective within the telepresence environment and not look beyond the field of view. One relatively simple solution, where the telepresence environment is based on a real three dimensional environment, is to simply use the head orientation sensors to cause a camera to track the orientation of the viewer. This has obvious limitations in that only one viewer can be in the telepresence environment at a time (since the camera can only track one viewer, and the other viewers will not typically be able to follow the head motions of the controlling viewer) and, also, prerecorded data cannot be used. Further, there is an inherent delay between a change in user viewing perspective and the time that it takes to realign the corresponding camera. These limitations greatly restrict the value of such systems.
One method for overcoming each of these limitations is to encode, either in real time or by pre-recording, a field of view largely equivalent to the entire range of motion vision of a viewer--that is, what the viewer would see if he moved his head in each permitted direction throughout the entire permissible range. For example, encoding substantially a full hemisphere of visual information would permit a plurality of viewers a reasonable degree of freedom to interactively look in a range of directions within the telepresence environment.
The difficulty with this approach is that most means for encoding such information distort, or warp, the visual data, so that the information must be corrected, or "de-warped" before a viewer can readily assimilate it. For example, a typical approach for encoding substantially a full hemisphere of information involves using a fish-eye lens. Fish-eye lenses, by their nature, convert a three dimensional scene to a two-dimensional representation by compressing the data at the periphery of the field of view. For the information to be viewed comfortably by a viewer in the VR environment, the visual data must be decompressed, or dewarped, so that it is presented in normal perspective as a two dimensional representation.
One solution to the distortion problem is proposed in U.S. Pat. No. 5,185,667 issued to Steven Zimmerman. The '667 patent describes an apparatus which effects camera control for pan, tilt, rotate and zoom while having no moving parts. Through the use of a fisheye lens and a complicated trigonometric technique, portions of the video images can be dewarped. However, the solution proposed by the '667 patent is impractical because it is insufficiently flexible to accommodate the use of other lenses besides a theoretically perfect hemispherical fisheye lens without the introduction of mathematical errors due to the misfit between the theoretical and the actual lens characteristics. This solution also introduces undesirable trigonometric complexity which slows down the transformation and is overly expensive to implement. This solution further maps each individual pixel through the complex trigonometric mapping formula further reducing the speed of the transformation from one coordinate system to another.
As a result, there has been a substantial need for a method and apparatus which can dewarp encoded wide angle visual data with sufficient speed and accuracy to permit a viewer to immerse himself in a VR or telepresence environment and look around within the environment while at the same time permitting other viewers concurrently to independently engage in the same activity on the same broadcast video signal. There has also been a need for a method and apparatus capable of providing such dewarping on a general purpose high speed computer.